The present invention relates to removing a coating from a superalloy substrate. In particular, the invention relates to systems and methods for improving the removal of a coating from a superalloy substrate.
It is advantageous to provide gamma/gamma prime bond coats for nickel base superalloys of the gamma/gamma prime type because this type of coating has demonstrated greater spallation resistance over conventional gamma/beta systems. Gamma/gamma prime alloys are solid solutions of the alloy with intermetallic compounds as a second phase. However, gamma/gamma prime coating provides difficulties in stripping without damage to the substrate due to the close similarities of the coating and the base material.
During operation, the coatings suffer environmental damage and need to be periodically replaced or repaired to extend the life of the gas turbine hardware. Because of the corrosion and oxidation products that form on the surfaces, it is necessary to completely remove and reapply the coatings in selected areas before placing the component back in service. Mechanical means of removing the coatings such as abrasive blasting or machining are not preferred because of cost and the chance of harming the underlying substrate.
The method of choice for those experienced in the art is chemical removal (or chemical stripping) wherein the coating to be removed is exposed to a solution that weakens and eventually dissolves the coating. However, care must be taken to avoid damage to the base material if replacement is to be avoided.